I have been learning a bit about visual memory as related to delays with my son's reading/fluency/spelling/grammar... I am wondering about these visual exercises out there and specifically if they work or are just hype. Any thoughts or experience?

I think it depends on what area you are working on and what type of exercises are being done. Both of my kids went through visual therapy. One was successful, one was not. The one that was not successful was because the therapy didn't target her real problem, which at the time we did not know.

You don't know until you try. :)